Storage of liquid hydrazine rocket fuels

ABSTRACT

Liquid hydrazine fuels are stored in maraging steel containers for rocket systems provided with a thin protective lining of a metal of the group consisting of cadmium, silver, aluminum, nickel, tungsten, tin and alloys of tin with cadmium, nickel, and lead whereby the rate of decomposition of the fuel is greatly retarded and the fuel can be safely stored for long periods.

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Ng et a1. 1451 Feb. 6, 1973 STURAGE OF LIQUID HYDRAZINE [56] References Cited ROCKET FUELS UNITED STATES PATENTS Inventors: Wahling H. Ng, Rockaway; William 3,262,823 7/1966 Sadowski et a1 .148/142 F. Lehman, Sparta, both of N..I.; 3,338,803 8/1967 DiBari ..1.1 17/71 M John P. Young, Gaithersburg, Md. 3,466,224 9/1969 Vaughn et al.... ....117/71 M 3.356252 12/1967 Petriello ..220/64 X [73] Assignee: The United States of America as represented by the Secretary of the Army rimary Examm r--Edward G. Whitby Attorney-Harry M. Saragovitz, Edward J. Kelly, Her- [22] Filed: May 28, 19 bert Berl and Victor Erkkila 21 App1.No.: 148,061 57 ABSTRACT 52 US. Cl. ..117/71 M, 117/97, 117/107," Liquid hydrazine fuels are Stored in maraging Steel 117/130 E, 117/160 R, 149/36, 149/109, containers for rocket systems provided with a thin 204/32 R, 204/145 R, 220/64 protective lining of a metal of the group consisting of [51] Int. Cl. ..B44d l/02 cadmium, silver, aluminum, nickel, tungsten, tin and [58] Field 0f rh----. 17/ 160 alloys of tin with cadmium, nickel, and lead whereby 117/71 149/36, the rate of decomposition of the fuel is greatly re- 204/32 R R tarded and the fuel can be safely stored for long periods.

11 Claims, 1 Drawing Figure STORAGE F LIQUID HYDRAZINE ROCKET FUELS The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to us of any royalty thereon.

BACKGROUND OF THE INVENTION The present invention relates to storage of liquid hydrazine fuels.

The high tensile strength (up to 300,000 psi) and hardness of 18% Ni maraging steels makes possible the fabrication of high pressure tankage systems, which possess less weight'and bulk than those made from lower density materials. These properties are desirable for material used to construct liquid propellant tanks for rockets as they increase the ratio of payload to total weight of a flight vehicle and thereby permit improved performance. Maraging steels have been employed as containers for solid propellants. However, their use in conjunction with liquid hydrazine type rocket fuels has encountered problems because of decomposition of the fuel in contact with the maraging steel, which generates gaseous decomposition products and dangerous pressures within the container.

Accordingly, a need has existed for a method for retarding the decomposition of hydrazine fuels in contact with maraging steels.

It has been proposed to coat the maraging steel with a metal which is relatively inert towards liquid hydrazine fuels. However, the choice of metals for this purpose is limited, since it is known that many metals react with or are dissolved by such propellant fuels. Further, in view of the passivity of maraging steels, it is difficult to produce a satisfactory coating thereon with a suitable metal by electrolytic methods. Also, the irregular interior surfaces and welds usually present in maraging steel tanks increase the difficulty of providing an adequate coating of the metal.

It is an object of this invention to provide a method for storing liquid hydrazine fuels in maraging steel containers, whereby the rate of decomposition of the fuel is greatly retarded and the fuel can be safely stored for long periods.

Another object is to provide a method of application of very thin protective coatings of certain metals on maraging steels, whereby containers and rocket tankage systems fabricated from maraging steels can be economically and reliably coated after assembly and the advantage of light weight, high strength maraging steels can be utilized in liquid fuel rocket systems.

Other objects will be obvious or appear from the following description of the invention.

DESCRIPTION OF THE INVENTION We have discovered in accordance with this invention that liquid hydrazine fuels can be protected against decomposition and hence can be safely stored in maraging steel containers by coating the surface of the container exposed to said fuel with a metal selected from the group consisting of cadmium, silver, aluminum, nickel, tin, tungsten and tin alloyed with a metal of the group consisting of cadmium, nickel and lead.

More specifically, we have found that by providing a thin coating ofa metal of the aforementioned class over the interior of the maraging steel container, liquid hydrazine fuels can be stored in such containers for long periods with very low buildup of pressure due to decomposition of the fuel into gaseous products and with negligible corrosion of the coating by the fuel. In contrast, a large, unacceptable pressure buildup is obtained when the fuel is stored under the same conditions in a maraging steel tank wherein the surface in contact with the fuel is bare maraging steel.

Liquid hydrazine fuels suitable for use in our invention include hydrazine, monomethyl hydrazine, 1,1- dimethyl hydrazine (unsymmetrical dimethyl hydrazine) and mixtures thereof.

Maraging steels as a class are high nickel steels oflow carbon content, whose strength is achieved primarily through aging a martensitic matrix. Especially high strength maraging steels contain, besides iron, substantial amounts, e.g., 10 to 20 percent by weight, of nickel together with lesser amounts of cobalt and molybdenum, and small amounts of titanium and aluminum, the cobalt, molybdenum, titanium and aluminum serving as hardening agents which increase the strength of the steel. Maraging steels containing significant amounts of cobalt or molybdenum, in view of their high strength to weight ratio, are particularly desirable for fabrication of rocket motor cases for liquid hydrazine fuels. Our invention is especially valuable for use with such maraging steels, since we have found that metallic cobalt and molybdenum greatly accelerate the decomposition of liquid hydrazine fuels.

The following illustrate maraging steels suitable for use in our invention:

Maraging Steel Nominal Chemical Nominal Yield Type Composition Strength Ni Co Mo Ti Al 18 Ni 300 18 9 5 0.7 .l 300,000 psi 18 Ni 250 18 7 5 0.5 .1 250,000 psi l8 Ni 200 18 8.5 3.5 0.2 .1 200,000 psi 18 Ni I 18 8 2 0.15 .1 180,000 psi l2-2Ni l2.5 8 4 0.2 .1 200,000 psi Maraging steel specimens were coated with a metal of the foregoing class as described in the following examples, and the resulting specimens together with control specimens of maraging steel and other metals were tested for their effect on the decomposition of hydrazine rocket fuel, as described below under Test Procedure". The accompanying drawing illustrates a glass apparatus used in the tests for measuring gas generated from decomposition of the fuel. The test results are set forth in Table 1 below.

Test Procedure In service, rocket fuels may be stored in deserts at temperatures that may reach F or in artic areas where temperatures may drop as low as 65F. Since elevated temperatures would be expected to cause maximum rates of decomposition of the fuel, the tests were conducted at 160F. The decomposition of the fuel results in the continuous generation of gas, which over a long period of time, could reach a pressure sufficient to rupture a tank. Since the desired storage life of the rockets is about 6 years, the tests were continued for a period of at least 1 year to predict long-term performance.

The glass apparatus illustrated in the drawing was employed for measuring gas evolved from decomposition of fuel. It consists of a bulb 1 connected via vertical tube 2, cross-arm tube 3 and downwardly extending vertical tube 4 to a manometer loop consisting of bulb 5 and tube 6 containing mercury 7. A glass frit 8 prevents accidental transfer of mercury to bulb 1 containing the test specimen 9 immersed in the fuel 10. The apparatus is strengthened by braces 11 and 12. The dotted extensions 13 and 14 of specimen bulb 1 and fuel inlet tube 2 resp. show the form of apparatus prior to loading.

The dotted extensions in the drawing show the form of the unit before loading. The unit in this form was tagged with an identification number and the following calibration measurements made: (a) Volume per unit length of the right-hand leg of the manometer. (b)

Total manometer head as a function of height of mercury above the zero point in the right-hand leg. (c) Volume per unit length of the specimen chamber. (d) Volume of the cross-hatched portion of the gas chamber.

These data, combined with manometer readings, are required for calculating the quantity of gas formed.

The unit was then cleaned by the following steps: (a) Submerge and soak in a nitric acid solution (1:1 dilution of cone HNO for 2 hours. (b) Rinse with distilled water. (c) Soak 2 hours in aqueous NH (1 part conc Nl-l plus 4 parts H O). (d) Rinse with distilled water. (e) Oven dry.

The unit was then clamped in an inverted position. The specimen to be tested (previously cleaned by usual pre-plating procedures, followed by a soak in the above NH; solution, rinsed and air-dried) was inserted into the specimen chamber through its open end. The specimen chamber was then sealed by fusing and drawing the glass. Adequate precautions were taken during this operation to avoid heating and oxidizing the specimen (Step-wise drawing with intermittent cooling, air blast cooling of the outside of the opposite end of the specimen chamber, and simultaneous flushing of the specimen chamber with nitrogen). The fuel inlet tube was then sealed at a point a few centimeters above the position of the seal shown in the drawing. The unit was then pumped down to a low pressure through the open end of the manometer tube and all seals were checked with a spark-type, high voltage leak tester. Leaks, if found, were repaired. For further leak-testing, mercury was then added to the manometer and the unit was pressurized with N using a 2 mm TFE tube pushed through the mercury column, to the limit of the manometer tube, thus exposing all fusion seals and joints to the gas. After about two weeks, if no evidence of a leak was observed the units were opened by breaking the fuel inlet tube just below its sealed tip and enough fuel was added to cover the specimen. A plastic syringe with its needle attached to a 2 mm-dia TFE tube was used to introduce the fuel into the lower end of the specimen bulb without wetting the wall of the inlet tube. A temporary closure of the inlet tube was then made with a TF E plug. The fuel was left in the unit about 1 week to leach possible residual impurities from the specimen and the interior of the unit. This fuel was then removed by use of the syringe and replaced with fresh fuel, again avoiding wetting of the upper end of the inlet tube. lf wetted at this point, it was sometimes difficult subsequently to obtain a leak-free fusion seal. The fuel inlet tube was then resealed by fusion at the position shown in the drawing. The seal was inspected under magnification. If perfect, the unit was flushed (alternately pressurized and depressurized) with N, by inserting a long, 2 mm-dia TFE tube through the open end of the manometer, through the mercury, and into the gas chamber above the mercury in the manometer bulb. The unit was then placed in the constant temperature bath to begin the test.

Measurement of gas generation.

A scale graduated in centimeters was attached to the manometer tube of the glass units to permit measurement of the height of the mercury at given times. From these values and the calibration data for the unit, pressure and gas volume in the unit were determined. 7

For the glass units, the equation wrlpl)/Pa gives the amount of gas evolved, measured at atmospheric pressure (p where V, and V are initial and later gas volume in the unit, respectively, and p and p are the corresponding pressures. The amount of gas evolved, as calculated from equation (1), is due in part to catalytic decomposition of fuel at the surface of the metallic specimen, and in part to decomposition of fuel at other locations, e.g., in the liquid itself, in the vapor phase, and at glass-fuel interfaces. Decomposition at these locations is referred to as background decomposition. It was determined in identical units except that no metal specimen was present AV due to background decomposition, which was found to be very small in the glass units, was subtracted from AV of equation (1 to obtain the volume of gas evolved due to the effect of the metallic specimen itself.

Since the rate of gas evolution due to contact of a given metal with the fuel is proportional to the area of the metal, catalytic activity may be expressed as a rate coeflicient as follows:

a given period will obviously be proportional to the rate coefficient of equation 2. It can be shown that P 10560) (rate coefficient) where P is gage pressure in psi after 1 year. The numerical factor takesaccount of time, tank surface, ullage and conversion from metric to English units. P is inversely proportional to ullage; thus if the ullage were 5 percent, the numerical factor and P would be doubled.

The following examples illustrate the invention:

Example 1 A maraging steel specimen approximately 1 cm. wide, 5 cm. long, 2mm. thick with a surface area of 15 cm was plated with cadmium as described below. The

specimen was cut from a sheet of heat-treated maraging steel of the following chemical composition in addition to iron: Ni 18, Co 9, Mo 5 and Ti 0.6%.

Because of its passivity due to substantial content of cobalt and molybdenum, maraging steel requires special preplating processing to activate its surface and remove oxide films which interfere with proper adhesion of a metal deposit. Consequently, the heavy heattreatment scale was first removed by mechanical abrasion and pickling in an aqueous mixture of concentrated sulfuric and nitric acids. After descaling, the maraging steel specimen was treated in the manner described belowto apply a nickel undercoat or strike with an acid nickel chloride solution, which is more reactive with the maraging steel surface than standard plating solutions. The treatment represents a modification of the procedure described in U.S.P. 338803, G.A.Di Bari.

l. Pumice scrub.

2. Water rinse.

3. Electropolish, until surface is smooth and clean, in

a solution of 20 percent (by wt) of H S 60 percent H PO 5 percent CrO percent H O. Temperature 40C (104E); anode current density, 7 A/dm; duration, 2 min.

4. Water rinse.

5. Remove smut, if necessary, by immersing for 1 minute in chromic sulfuric acid: CrO 50 g/l; H SO 10 g/l; room temperature.

6. Water rinse.

7. Strike in an acid nickel chloride solution: NiCl -6 H 0, 240 g/l; HCI (conc), 125 ml/l; room temperature; cathode current density, 2 A/dm; plating period, 1 min. Immerse for l min before applying current.

8. Rinse and transfer quickly to the desired plating bath.

The thickness of the final deposit was determined by weighing the specimen before step 1 above and after plating, after applying corrections for weight changes due to steps 3 and 7. The weight after plating also served as a basis for determining weight loss due to corrosion resulting from subsequent exposure of the specimen to the fuel.

The cadmium plate was deposited on the nickel undercoat (estimated thickness of the nickel strike was microinches) produced in steps 7 and 8 using the cyanide plating bath and conditions described below:

CdO 22.5 g]! NaCN 99.6 g]! NaOH 14.0 g/l Na,C0, 4.0 g/l Room temperature 20 AJft. Thickness of Cd coating 0.002 in.

After plating the specimen was rinsed with water and dried.

Example 2 A maraging steel specimen having a cadmium coating of 0.0005 in. thickness was prepared as described in Example 1.

Example 3 A maraging steel specimen having a cadmium coating of 0.000l in. thickness was prepared as described in Example 1.

Example 4 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike; all as described in Example 1. The specimen was then transferred without rinsing to a Watts nickel bath and electro-plated at 2 A./dm at 50C.

Example 5 NiCl,-6H O 30 g/l Sodium hydroxy acetate 50 gll Sodium hypophosphite l0 g/l pH 4 to 4.5 Temperature C Thickness, Ni coating 0.002 inch Example 6 A maraging steel specimen coated with electroless nickel, identical with that obtained in Example 4, was heated to 800C. to simulate the effect of a welding operation after plating.

Example 7 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then electroplated in known manner with tin.

Example 8 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then electroplated with silver from a conventional bath in known manner.

Example 9 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then electroplated in known manner with aluminum.

Example 10 A maraging steel specimen of the foregoing type was given a surface preparation according to the procedure described in Example 5, and then dipcoated with a bath of molten solder consisting of 50 percent lead and 50 percent tin by weight.

Example 1 l A maraging steel specimen of the foregoing type was given a surface preparation as described in Example 5 and then dip-coated with a bath of molten alloy consisting of 50 percent tin and 50 percent cadmium by weight.

Example 12 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1 and then coated with a nickeltin alloy consisting of 65 percent tin and 35 percent nickel by electroplating same from a conventional alloy electroplating bath in known manner.

Example 13 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then electroplated with chromium from a conventional bath in known manner.

Example 14 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then electroplated with zinc from a conventional bath in known manner.

Example 15 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then coated with tungsten by vapor deposition in known manner.

Example 16 A maraging steel specimen of the foregoing type was given a surface preparation and a nickel strike as described in Example 1, and then electroplated with coatings on maraging steel of cadmium, silver, tin, nickel, aluminum, tungsten and alloys of tin with cadmium, nickel and lead effectively prevent the development of pressures exceeding the aforesaid limits due to decomposition of the mixed hydrazine fuel. Further, coatings of said metals and alloys are not appreciably corroded by the hydrazine fuel. Although zinc exhibits a very low rate of decomposition of the fuel, it is severely corroded thereby and is hence unsuitable for use as a container for hydrazine fuel in rocket systems.

Cadmium and electroless nickel are the most practicable and preferred of the coatings of this invention.

Thus, cadmium exhibits essentially the lowest rate of decomposition of the mixed hydrazine fuel and its rate of corrosion thereby is sufficiently low as not to deter its use in rocket systems; also, the cadmium cyanide bath is easily operated and possesses good throwing power, which is an advantage when plating irregular tank contours. Electroless nickel coating exhibits a very low rate of decomposition of the hydrazine fuel and undergoes negligible corrosion thereby; it can be readily applied without an internal anode which is an important advantage in plating tanks of complicated designs into which insertion of an internal anode may be difficult. Also, the ability of the electroless nickel bath to produce a coating of uniform thickness, regardless of irregularities in tank contour, is also important. Further, an electroless nickel coating on maraging steel, heated in air at 800C. to simulate the effect of a welding operation, exhibits about the same rate of decomposition as an unheated specimen coated with electroless nickel. Hence, heat treatment and welding of such coatings do not increase their catalytic activity toward decomposition of hydrazine fuels. Solder (/50 lead-tin alloy) exhibits a hydrazine fuel decomposition rate coefficient of almost zero, is not appreciably corroded thereby and can be applied to maraging steel by dip-coating or from a known alloy Cohan in known mane 40 platlng bath. However, since presently available alloy TABLE 1 [Data on decomposition of mixed hydrazine-monomethyl hydrazine fuel at 160 F.]

b Calculated Rate tank Time 7 I coeflipressure Area of under a Gas cieni: a! 1' Example Specimen (coatings on maraging steal are 0.002 in. thick specimen, test evolved, (cmfi/day/ one year number unless otherwise specified) em. (days) cm. cm?) (p.s.i.g

1 Cadmium -14. 7 894 2. 6 0. 00020 2 2 Cadmium (0.0005 in.). 9. 4 1034 18. 6 0. 0019 20 3 Cadmium (0.0001 in 14. 4 283 12. 4 0. 00030 32 4 Nickel l4. 0 685 29. 9 0. 0031 33 5.. Electroless nickel 22. 2 1067 23. 7 0. 0010 11 Electroless nickel heated to 800 C 12. 2 585 8. 8 0. 0012 13 T 13. 0 799 31. 8 0. 0031 32 14. 6 905 4. 6 0. 00035 4 14 194 13. 1 0.0048 51 14. 3 299 0. 4 0. 00029 1 l4. 0 238 10. J 0. 0033 35 24. 0 358 61 0. 0000 03 I7. 0 482 113 0. 0201 213 l4 l5. 11 MI 16.4 0.0020 31 15.. 24. 8 300 30. 7 0. 0002 (ill 16 o 10. 1 11m 0. 04 u, not; Molybdenum (solid metal specimen) 4. 8 368 217 0. 123 1, 300 Maraging steel (control) (so id metal specimen 17. 0 371 485 0. 007 l, 030

e Cumulative total, corrected for background rate and to 1 atm. pressure.

b Based on a tank in the form of a'cube, 1 ftlvolume, 10% tillage.

Discussion of Test Results For reasons of safety the internal pressure buildup in a rocket tankage system generally cannot be permitted to exceed 100 psi per year or a total of 500 psi for 5 years. The tabulated test results show that very thin baths possess poor throwing power, it would be difficult to electroplate an alloy coating with uniform thickness on the interior surface of a tank of irregular form.

To confirm the protective action of the coatings of this invention under practical conditions, long term storage tests were conducted with internally coated maraging steel cylinders containing mixed hydrazinemonomethyl hydrazine fuel. For this purpose maraging steel cylinders 26 inches long and 3.5 inches l.D. (about one-half the size of actual rocket fuel tanks) were completely coated internally with cadmium, nickel and 50/50 lead-tin solder. Prior to coating the interior surface, the cylinder was given a pretreatment comprising descaling, electropolishing and striking with nickel, as follows: The cylinder was charged through an opening at one end thereof with a pickling solution consisting of 500 ml. conc. sulfuric acid, 430 ml. conc. nitric acid and 200 ml. water together with 1 liter of granite chips of about inch mesh size. The cylinder was closed with a plug and rotated end-overend at about 6 RPM for 6 hours, with periodic rotation on its longitudinal axis. It was then emptied, rinsed with water and dried, and electropolished minutes at 40-60C. and 7 A/dm with the following electropolish solution:

%by weight sulfuric acid 20 phosphoric acid 60 chromium trioxide 5 water The cylinder was then rinsed 5 minutes with warm tap water and then given a nickel strike as described in Example above.

The cadmium and nickel electroplating baths used are described in Examples 1 and 4 above. The plating solution was circulated by pumping it from a reservoir through a filter, thence through a tubular anode inserted through the top of the vertically positioned cylinder and extending almost to the bottom thereof, and finally out of the cylinder through an outlet at the top adjacent the anode back to the reservoir. The electroless nickel coating was applied in similar manner by using the surface preparation and bath conditions described in Example 5 above, except that no current was applied to the aforesaid anode tube and a hot water bath was employed to maintain the near boiling temperature required for plating electroless nickel.

The coated cylinders thus obtained were charged with the mixed hydrazinemethyl hydrazine fuel, leaving 10 percent free space (ullage), and stored at 100F in a temperature controlled chamber, with cycling to -65F and +160F (maximum military requirements) for 1 day at each temperature level every 4 weeks. During temperature cycling the cylinders were also transported by truck from one building to another building to simulate actual transfer. The storage tests were carried out for a period of 2 years, during which the pressures in the cylinders did not exceed 35 psig per year, indicating the effectiveness of the coatings. The pressure buildup was due to the temperature to which the cylinders were exposed and not to gaseous decomposition products of the fuel.

Another series of maraging steel cylinders of the aforementioned type, coated in the manner described above with various thicknesses of electroplated cadmium, electroplated nickel, electroless nickel and dipcoated 50/50 lead-tin solder, were filled to 10 percent ullage with the mixed hydrazine-monomethyl hydrazine fuel and submitted to long term storage tests under the same temperature cycling conditions as described above. The test results set forth in Table 2 reveal that all coatings were satisfactory except the 0.5 mil thickness of electroless nickel, which did not prevent substantial decomposition of the fuel (160 psig pressure buildup after 1 V2 months at I00F.) However, negligible pressure was generated in a cylinder wherein the coating of electroless nickel was 0.88 mil thick, showing the importance of adequate coating thickness.

Table 2 Cylinder Coating Thickness Time Pressure No. Material (mils) (months) (psig) l electroplated nickel 4 24 65 2 electroless nickel 3 24 3 electroless nickel 0.88 12 45 4 electroless nickel 0.5 1.5 160 (test termina ted) 5 cadmium 5.5 24 6 cadmium 1.2 12 50 7 50/50 leadtin alloy 8 6 40 All tanks were initially pressurized to 30 psig with nitrogen.

The coatings of this invention can be similarly applied to metals other than maraging steels possessing high strength/weight ratio, which are not compatible with liquid hydrazine fuels to produce containers suitable for use in rocket systems for storing liquid hydrazine fuels.

We wish it to be understood that we do not desire to be limited to the exact method and detail of construction described for obvious modification will occur to persons skilled in the art.

We claim:

1. A method for storing liquid hydrazine fuels, which comprises maintaining said fuel in a container wherein the container wall in contact with the fuel consists of maraging steel coated with a metal of the group consisting of cadmium, silver, tin, nickel, aluminum, tungsten and tin alloyed with a metal of the group consisting of cadmium, nickel or lead.

2. The method according to claim 1, wherein the fuel is selected from the group consisting of hydrazine, monomethyl hydrazine, l,l-dimethyl hydrazine and mixtures thereof.

3. The method according to claim 1, wherein the maraging steel contains 10-20 percent nickel, 7-9 percent cobalt and 2-5 percent molybdenum.

4. The method according to claim 1, wherein the fuel consists essentially of a mixture of hydrazine and monomethyl hydrazine.

5. The method according to claim 1, wherein the metal coating is about 1 to l0 mils in thickness.

6. The method according to claim 1, wherein the metal is cadmium.

7. The method according to claim 1 wherein the metal is electroless nickel.

8. The method according to claim 1, wherein the metal is coated on a nickel undercoat on the maraging steel.

9. in a rocket tankage system the improvement which comprises a container for storing liquid hydrazine fuels, wherein the container wall in contact ii 12 with the fuel is composed ofmaraging steel coated with 10. A container according to claim 9 wherein the a metal of the group consisting of cadmium, silver, tin, maraging steel is coated with cadmium. nickel, aluminum, tungsten and tin alloyed with a metal 11. A container according to claim 9 wherein the of the group consisting of cadmium, nickel and lead. maraging steel is coated with electroless nickel. 

1. A method for storing liquid hydrazine fuels, which comprises maintaining said fuel in a container wherein the container wall in contact with the fuel consists of maraging steel coated with a metal of the group consisting of cadmium, silver, tin, nickel, aluminum, tungsten and tin alloyed with a metal of the group consisting of cadmium, nickel or lead.
 2. The method according to claim 1, wherein the fuel is selected from the group consisting of hydrazine, monomethyl hydrazine, 1, 1-dimethyl hydrazine and mixtures thereof.
 3. The method according to claim 1, wherein the maraging steel contains 10-20 percent nickel, 7-9 percent cobalt and 2-5 percent molybdenum.
 4. The method according to claim 1, wherein the fuel consists essentially of a mixture of hydrazine and monomethyl hydrazine.
 5. The method according to claim 1, wherein the metal coating is about 1 to 10 mils in thickness.
 6. The method according to claim 1, wherein the metal is cadmium.
 7. The method according to claim 1 wherein the metal is electroless nickel.
 8. The method according to claim 1, wherein the metal is coated on a nickel undercoat on the maraging steel.
 9. In a rocket tankage system the improvement which comprises a container for storing liquid hydrazine fuels, wherein the container wall in contact with the fuel is composed of maraging steel coated with a metal of the group consisting of cadmium, silver, tin, nickel, aluminum, tungsten and tin alloyed with a metal of the group consisting of cadmium, nickel and lead.
 10. A container according to claim 9 wherein the maraging steel is coated with cadmium. 